Pivotal bone anchor assembly with upper and lower shank head-engaging spherical surfaces spaced apart from a rod-engaging pressure insert

1. A pivotal bone anchor assembly for anchoring to a patient bone and coupling with an elongate rod via a closure, the pivotal bone anchor assembly comprising:

a shank having a longitudinal axis, a head with a partial spherical shape defining a hemisphere plane perpendicular to the longitudinal axis with an outer spherical surface extending above and below the hemisphere plane, and an anchor portion extending downwardly from the head for fixation to the patient bone;

a receiver having a base, a pair of integral upright arms extending upward from the base to define an open channel configured to receive the elongate rod, and an axial bore centered around a longitudinal axis, the axial bore communicating with a bottom surface of the receiver base through a bottom opening and extending upwardly through the open channel to a top surface on each of the receiver upright arms, the axial bore including a non-threaded recess with a downwardly-facing surface and an upwardly-opening partial spherical seating surface disposed about the bottom opening and configured to receive a lower portion of the shank head outer spherical surface to provide for pivotal movement between the shank and the receiver;

an insert configured to be top loaded into the receiver bore and having a second pair of upright arms with upper outer surfaces at least partially positionable within the receiver recess and into a biased overlapping engagement with the receiver recess downwardly-facing surface, prior to the assembly being locked by the closure, so as to prevent the insert from moving back up within the receiver, the insert further including an upwardly-facing rod engaging surface between the second pair of upright arms; and

a downwardly-opening partial spherical surface disposed within the receiver axial bore and configured to engage an upper portion of the shank head outer spherical surface, the downwardly-opening partial spherical surface being separate from and spaced below a bottom of the insert, the downwardly-opening partial spherical surface including a circular edge circumscribing the longitudinal axis of the receiver, the circular edge having a diameter smaller than the lamest diameter of the shank head,

wherein when the pivotal bone anchor assembly is fully assembled, the downwardly-opening partial spherical surface and the receiver upwardly-opening lower partial spherical seating surface are configured to have frictional engagement with the shank head outer spherical surface so as to provide a non-floppy pivotal relationship between the shank and the receiver prior to the elongate rod and the closure being positioned within the receiver open channel.

2. The pivotal bone anchor assembly of claim 1 , wherein the upwardly-opening partial spherical seating surface of the receiver is configured to continuously frictionally engage around an entire circumference of the shank head outer spherical surface below the hemisphere plane when the shank head is disposed within the receiver and the shank longitudinal axis and the receiver longitudinal axis are co-aligned with respect to each other.

3. The pivotal bone anchor assembly of claim 1 , wherein the downwardly-opening partial spherical surface is integral with the receiver axial bore.

4. The pivotal bone anchor assembly of claim 3 , wherein the downwardly-opening partial spherical surface is continuous with the upwardly-opening partial spherical seating surface of the receiver.

5. The pivotal bone anchor assembly of claim 1 , wherein a bottom surface of the insert is configured to engage the shank head outer spherical surface above the downwardly-opening partial spherical surface.

6. The pivotal bone anchor assembly of claim 1 , wherein the downwardly-opening partial spherical surface is configured to be frictionally engageable around an entire circumference of the shank head outer spherical surface above the hemisphere plane when the shank head is disposed within the receiver and the shank longitudinal axis and the receiver longitudinal axis are co-aligned with respect to each other.

7. The pivotal bone anchor assembly of claim 1 , wherein the insert upright arms further include laterally projecting portions on which are located the upper outer surfaces.

8. The pivotal bone anchor assembly of claim 1 , wherein the insert includes a central through-bore.

9. The pivotal bone anchor assembly of claim 1 , wherein the insert is configured to be twisted into place within the receiver bore.

10. The pivotal bone anchor assembly of claim 1 ,

wherein the insert second pair of upright arms extend upward from an insert base having a first outer diameter, and

wherein the insert base further includes a downwardly-extending lower portion having a second outer diameter less than the first outer diameter.

11. The pivotal bone anchor assembly of claim 1 , wherein the insert includes a bottom surface configured to be spaced apart from the downwardly-opening partial spherical surface when the downwardly-opening partial spherical surface is engaged against the shank head outer spherical surface.

12. The pivotal bone anchor assembly of claim 1 , wherein the receiver upright arms further include upwardly-projecting break-off extensions.

13. The pivotal bone anchor assembly of claim 1 , wherein the receiver upright arms further include lateral outer surfaces adjacent the top surface on each upright arm, the lateral outer surfaces having non-threaded horizontally elongated radiused tool attachment grooves extending to both a front side surface and a back side surface on each arm, the grooves being symmetrically located below the receiver upright arm top surfaces.

14. The pivotal bone anchor assembly of claim 1 , wherein the receiver upright arms further comprise inner sidewall surfaces mateable with the closure.

15. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated along its longitudinal axis.

16. The pivotal bone anchor assembly of claim 1 , wherein the shank anchor portion includes multi-start bone engaging helically wound threads.

17. The pivotal bone anchor assembly of claim 1 , wherein the shank is configured to be downloaded into the receiver bore until the shank head is pivotally engaged against the receiver lower partial spherical seating surface.

18. The pivotal bone anchor assembly of claim 1 , wherein the shank head is configured to be uploaded through the receiver bottom opening and into the receiver axial bore.

19. The pivotal bone anchor assembly of claim 18 ,

wherein the assembly further comprises a retainer attachable to a shank proximal end capture structure integral with the shank anchor portion, and

wherein an outer surface of the retainer at least partially defines the outer spherical surface of the shank head.

20. The pivotal bone anchor assembly of claim 1 , further comprising the closure, and wherein the closure has a single piece construction with a splay-control outer thread form configured to threadably engage inner sidewall surfaces of the receiver upright arms.

21. The pivotal bone anchor assembly of claim 20 , wherein the closure splay-control outer thread form further comprises a reverse angle thread.

22. The pivotal bone anchor assembly of claim 20 , wherein the closure splay control outer thread form further comprises one of a square shaped thread and a buttress type of thread.

23. The pivotal bone anchor assembly of claim 20 , wherein the closure includes an upwardly-extending break-off tool attachment structure configured to drive the closure.

24. The pivotal bone anchor assembly of claim 20 , wherein the closure includes a substantially planar bottom surface configured to engage the elongate rod.

25. The pivotal bone anchor assembly of claim 24 , wherein the closure bottom surface further comprises the bottom surface of a downwardly-extending substantially cylindrical bottom protrusion having an outer diameter less than an inner diameter of the splay-control outer thread form.

26. The pivotal bone anchor assembly of claim 20 , wherein the closure includes a multi-start helically wound splay-control outer thread form with two start structures near a lower end of the closure and disposed diametrically opposite to each other.

27. The pivotal bone anchor assembly of claim 26 , wherein the start structures have a bottom chamfered surface tapering outwardly and upwardly.

28. The pivotal bone anchor assembly of claim 26 , wherein the start structures have a leading face with a concave surface portion and a convex surface portion.

29. The pivotal bone anchor assembly of claim 28 , wherein the concave surface portion has a portion with a first radius of curvature and the convex surface portion has a portion with a second radius of curvature that is substantially equal to the first radius of curvature.

30. The pivotal bone anchor assembly of claim 1 , further comprising the closure, and wherein the closure includes outer dual start helically wound threads and the receiver pair of upright arms include discontinuous dual start helically wound threads, the closure configured to be rotatably positioned between the upright arms such that the closure dual start threads substantially simultaneously threadably engage the receiver discontinuous dual start threads on each of the upright arms.

31. The pivotal bone anchor assembly of claim 30 , wherein each start of the closure dual start threads includes a start structure angularly displaced apart substantially 180 degrees with respect to each other about a longitudinal axis of the closure.

32. The pivotal bone anchor assembly of claim 28 , wherein the concave surface portion is adjacent a root of the splay-control outer thread form and the convex surface portion is adjacent a crest of the splay-control outer thread form.

33. The pivotal bone anchor assembly of claim 1 , wherein the insert has a lower portion with a first outer diameter and an upper portion with a second outer diameter larger than the first outer diameter.

34. The pivotal bone anchor assembly of claim 33 , wherein the first outer diameter is less than a diameter of the receiver axial bore extending upwardly through the open channel to the top surface of each upright arm of the receiver and the second outer diameter is greater than the axial bore diameter extending upwardly through the open channel.

35. The pivotal bone anchor assembly of claim 1 , wherein the downwardly-opening partial spherical surface is continuous along a circumference surrounding the longitudinal axis of the receiver.

36. The pivotal bone anchor assembly of claim 1 , wherein the downwardly-opening partial spherical surface is formed on a resilient material.